Leading 6-2 from the afternoon session, Selby rattled off the opening two frames of the evening session to put himself within one frame of the final.
However Walden posted breaks of 50, 62 and 85 to cut the arrears to 8-5 but Selby produced a match-winning break of 129 to seal his spot in the final where he will face Neil Robertson.
"Ricky had chances but he didn't take them and I was just picking up the pieces,” said Selby following the win.
"I probably played at 50-60% and missed balls with some amateurish play. I don't know why, perhaps it was about concentration, but I can't afford to make those mistakes against Neil."
The winner of Sunday's final will collect a cheque for £150,000.
First session report
Early runs of 69 and 44 had given Selby a two-frame advantage before Walden came to the table 51 behind to construct a break of 56 to halve the deficit.
Selby ground out frame four to take a 3-1 lead to the mid-session interval, but last season's World Championship semi-finalist again cut the arrears with contributions of 43 and 18 to take frame five.
Selby took the next three frames – including his 147 in frame seven - to go to the interval with a commanding lead.
Selby said of his maximum: "Up until the green I had played pretty much the perfect break, but then there was some tension because the brown only went to one pocket and it was hard work from then on.
"It was a great moment, but I am still involved in a tough semi-final which isn't over.
"There is big prestige doing it on TV in such a big tournament. The money wasn't on my mind!"
Selby will pocket a rollover 147 prize fund of £55,000, plus the tournament high break prize of £4,000 - so long as none of the other three men still left in the tournament don't produce their own maximum.